Effect of potential formation on the electrochemical behaviour of a highly alloyed austenitic stainless steel in contaminated phosphoric acid at different temperatures

The electrochemical behaviour of the highly alloyed austenitic stainless steel UNS N08031 (Alloy 31) in a contaminated phosphoric acid solution is studied using potentiodynamic curves, EIS and Mott–Shottky. The relative stability of the films formed on Alloy 31 has been studied after a pre-passivated treatment at 0.3, 0.5, 0.8 and 1 VAg/AgCl, potentials within the passive domain. The protection of Alloy 31 was provided by the inner oxide film, while the outer film was more defective. The electronic-semiconducting properties of the passive films have been correlated to corrosion resistance. Passivated Alloy 31 at 0.8 VAg/AgCl showed lower concentration of charge carriers, which beneficially affects the protecting and electronic properties of the passive oxide film.

► Impedance parameters vary depending on the applied potential of film formation.
► Protective properties were observed to increase with formation potential up to 0.8 V.
► The proximity of transpassive region affected to the stability of the passive film.
► Mott–Schottky plots showed the semiconductive properties of Alloy 31.